Note: This post has been updated since it was originally published to reflect compatibility with third party chargers.

BenQ is a brand you’re probably familiar with as a manufacturer of computer monitors and home theater projectors. It also makes the WiT --the most expensive LED desk lamp I’ve every tested. The company would like music lovers to now that it’s also in the portable speaker game. But as with many of its products, BenQ is taking a very unique approach. I just wrapped up testing the treVolo S, billed as “the world’s smallest Bluetooth electrostatic speaker.”

Electrostatic speakers are a high-tech alternative to traditional magnetic cone drivers. They are flat, and use an electrical current to vibrate a thin membrane sandwiched between two plates. The key advantage of this design is high accuracy in sound reproduction, with far less distortion than traditional speaker design. Disadvantages include poor bass response and a limited “sweet spot” listening area.

Electrostatic speakers have been around for decades, but remain relatively uncommon. When you find them, they tend to be in higher end audio systems and they're usually large speakers. BenQ launched the treVolo series of speakers in 2014, bringing electrostatic speaker technology to a Bluetooth portable speaker for the first time. The company tackled the bass deficiencies in the technology by incorporating traditional cone woofers in a hybrid design.

With the treVolo S, the company downsized its electrostatic hybrid speaker, making it more portable than the original (reviewed by Forbes contributor Geoffrey Morrison) and the followup treVolo 2. At $199, it’s also a relatively affordable option for anyone looking for an audio system that employs electrostatic technology.

The treVolo S charges via a micro USB port.Brad Moon

First Impressions

BenQ’s design team has put together a portable speaker that looks like nothing else out there.

Out of the box, the treVolo S is the size and shape of a brick. Constructed of aluminum and plastic, it’s heavy and features premium touches including dual, vertically stacked drivers with honeycomb black grills, ringed in tasteful copper trim. It looks and feels like a premium piece of audio gear, with little resemblance to other portable Bluetooth speakers.

Where things get really interesting is those electrostatic panels. They’re thin --less than 1/4-inch in thickness. They fold flat to the sides of the speaker for carrying, but when in use you flip them out 45 degrees. The form factor is now a pair of small drivers housed in a six-inch tall tower (with buttons on top), framed by a pair of thin rectangular panels that extend the speaker’s width to 8.5-inches. Unfolding the panels also reveals a pair of passive radiators that fire out the side of the speaker.

A rubberized base keeps everything stable despite the narrow footprint and tilts the works upward slightly. On top are nicely responsive audio control and power buttons, and two LED indicators that show connection status and battery level.

Visually, it’s a striking design.

Audio Performance and 3D Sound

So the million dollar (or at least $199) question is whether the audio produced by treVolo S lives up to expectations.

This was my first experience working with an electrostatic speaker design and I have to say, I found the treVolo S performance was significantly different compared to the traditional speakers I usually work with. In particular, high frequency sounds were reproduced with exquisite detail. Bass, on the other hand, could be a little underwhelming. The overall effect was an almost clinical level of precision --more accurate and balanced than a typical portable speaker, but also less warm.

A feature that saves the day is BenQ’s proprietary 3D Sound mode. This feature is advertised as “increasing the dimensions of the listening space without altering the original sound waves.” In practice, it’s an EQ setting, one that made a noticeable improvement --including a little more bass kick-- while still maintaining impressively detailed audio and offering more depth. All without sounding processed.

Simple Minds’ “New Gold Dream” offers a good example of the treVolo S in action. Vocals and synths pop, as does percussion. There are details in there that are lost on many speakers. But the bass that drives this song left me wishing for more low end punch. Going to another extreme, on The Allman Brothers Band’s “Midnight Rider” the treVolo excelled. You could practically hear the fingers strumming on the acoustic guitar and the reverb on the vocals was outstanding --especially in 3D mode-- but the bass and conga drums were just a little less pronounced than I would have liked.

Another of the limitations of electrostatic speaker technology is a reduced listening “sweet spot” and I did notice this with the treVolo S. Set on the workbench in my office --at ear height, well away from walls and only six feet from my chair-- it sounded fantastic. Listen to it while standing, off to the side, or at a greater distance and there was a noticeable drop-off in high frequency detail. The electrostatic panels drive audio in both directions, so place it too close to a wall and the sound quality drops. On the other hand, placed in a corner (but not too close to the walls), low frequency performance improves.

Top view shows buttons, LED indicator lights and the extended panels.Brad Moon

So positioning and the location of the listener are extremely important, making the placement of the treVolo S finicky compared to a run of the mill portable speaker.

The speaker’s maximum volume was also less than I would have hoped for although to its credit, the treVolo S is one of the very few speakers I’ve tested that can be played at maximum volume and still maintain its composure. Most turn into a cacophony of distortion, buzzing and ugly noise as you reach the far end of the volume range. Not so with the treVolo S. It’s enough to fill my small office with sound, but the extra oomph isn’t available when a great song comes on and I want to crank it up. Then again, this is a smaller version of the treVolo 2, so if providing music for a larger room, you have an option --it’ll just cost you more...

treVolo S Key Specs

Dual 1.5-inch, 12W woofers

Two passive radiators

Dual electrostatic diaphragm panels

Dual amplifiers

Frequency response 60 Hz to 20 kHz

3D mode

Battery life rated at 18 hours

Micro USB port for charging + direct input from a PC or device to internal DAC

Bluetooth 4.2, NFC

LED battery/connection indicators

3.5mm Aux input

Supports Duo mode with second speaker

USB charger and carrying bag included

Weighs 2.2 pounds

Battery Life and Portability

BenQ designed the treVolo S to be portable. The integrated Lithium-ion battery is rated at up to 18 hours of playback.

The treVolo S folds up for portability and offers 18-hour battery life, but you wouldn't want to drop it or risk it getting splashed.Brad Moon

During testing, I actually found my review unit exceeded 18 hours in one session. I wasn’t always playing the music at high volumes, but I hit 20 hours. It’s a very dense speaker, but it does fold up for carrying and BenQ included a cloth bag. That portability is tempered by a few realities, though... As mentioned, positioning is critical and BenQ also recommends a flat and stable surface. In addition, the speaker isn’t water resistant. I wouldn’t consider it a candidate for the deck, but it can be easily moved from room to room, or stowed and carried to a party.

The treVolo S charges and is powered via Micro USB. The instruction manual cautions against using power adapters other than the supplied charger, but BenQ assured me that the treVolo S can be safely used with a Micro USB cable and any UL-approved 5V charger you may have on hand for your smartphone or tablet.

A Somewhat Useless App

Like many wireless speakers, the treVolo S has an app. But it’s pretty underwhelming. Using an iPhone, every time I launched the app or powered up the speaker, the app prompted me for a quick push of the speaker’s Bluetooth button to connect (even though it was paired to the phone). Once connected it shows battery remaining, has a toggle for 3D sound and lets you pair two treVolo speakers for stereo sound. A help button displays the buttons with labels... It also shows the speaker’s firmware version.

With LED battery level indicators onboard and manually switching on 3D Sound available at the push of a button on the speaker, I found no need to use the app.

Should You Buy It?

This is a tough question, because the treVolo S is a very unusual speaker.

If you are shopping for a portable, wireless speaker that can take a bit of abuse --bumping around and the occasional splash-- the treVolo S is not that speaker. There are plenty of choices, many of which are half the BenQ speaker’s price. It’s also not likely to satisfy fans of booming bass or loud volume. If you want a portable that can be set just about anywhere, it’s also a pass. The treVolo S needs to be positioned perfectly to get the most out of its capabilities.

In addition to the detailed sound of its electrostatic speakers, the BenQ treVolo S is a striking looking audio device.Brad Moon

There are some scenarios where BenQ’s speaker is ideal, though. If you want a speaker that looks different, well it’s going to be tough to find a more unique looking portable than the treVolo S. Not just different, it also has a premium build and looks more expensive than its $199 price tag. In other words, it’s an option for those searching for a piece of audio gear that makes a visual statement. Outside of the novelty factor, the ideal audience for the BenQ treVolo S is a serious music listener, someone who values balanced and detailed audio --free of the bass-heavy signature that’s common in most portable speakers-- who also wants a compact, portable package.

Disclosure: BenQ provided a speaker for evaluation but had no input into this review.

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